Human faces can signal just four basic emotions: study

Turns out our exes were right -- we're even less able to show our emotions than we thought.

In a newly published study, researchers from the University of Glasgow found that the human face was capable of displaying only four distinct types of emotions. Previously, researchers believed the number to be a whopping six.

In the study, which was published in Current Biology, researchers studied the reactions of people who were shown computer-generated facial expressions. The participants were then asked to identify the emotion on display from six choices: happiness, sadness, fear, anger, surprise, and disgust.

The researchers found that participants initially reacted similarly to expressions of anger and disgust, which are both signaled with a wrinkled nose. Ditto for surprise and fear, which both feature wide eyes.

Smithsonian.com explains that "as the expressions developed, though, participants were able to distinguish between them, but only over time, suggesting that differences in anger, disgust, surprise, and fear are the result of social evolution rather than biological."

Lead researcher Rachel Jack told BBC News, "Our results are consistent with evolutionary predictions, where signals are designed by both biological and social evolutionary pressures to optimise their function."

"What our research shows is that not all facial muscles appear simultaneously during facial expressions, but rather develop over time supporting a hierarchical biologically-basic to socially-specific information over time."

BBC News reports that the researchers intend to further develop their study by examining how emotions are interpreted via facial expressions in different cultures.